Process for upgrading low-quality wood

Abstract

A process for upgrading low-quality wood including a softening stage, wherein one or more sections of low-quality wood are heated, in the presence of an aqueous medium and at a pressure which is at least the equilibrium pressure of the medium at the operating temperature, to a temperature in the range of from about 120° C. to about 160° C. and maintaining the temperature until the temperature difference between the center and the outer parts of the sections is less than about 20° C., a dewatering stage and a curing stage.

What is claimed is: 
     
       1. A process for upgrading low-quality wood to high-quality wood comprising: a) a softening stage, wherein one or more sections of low quality wood are heated in the presence of an aqueous medium and at a pressure which is at least the equilibrium pressure of said medium at the operating temperature, to a first temperature in the range of from about 120° C. to about 160° C. and maintaining said temperature until the temperature difference between the center and the outer parts of the sections is less than about 20° C. and then heating to a second temperature in the range of from about 160° C. to about 240° C. for not more than one hour until the temperature difference between the center and the outer parts of the sections is less than about 20° C., b) a dewatering stage, and c) a curing stage. 
     
     
       2. The process of claim 1 wherein the sections are heated to a first temperature in the range of from about 130° C. to about 145° C. 
     
     
       3. The process of claim 2 wherein the second temperature is in the range of from about 170° C. to about 220° C. 
     
     
       4. The process of claim 3 wherein the softening stage is conducted at a pressure which is higher than the equilibrium pressure at the operating temperature. 
     
     
       5. The process of claim 4 wherein the temperature between the center and the outer parts of the sections is not more than about 10° C. 
     
     
       6. The process of claim 4 wherein the second temperature is maintained for a period of time from about 0.1 to about 0.75 hour. 
     
     
       7. The process of claim 6 wherein the heating is effected by means of steam. 
     
     
       8. The process of claim 7 wherein the sections to be treated have a moisture content in the range of from about 50% to about 60% by weight. 
     
     
       9. The process of claim 8 wherein the sections are cooled to a temperature below about 100° C. before being dewatered. 
     
     
       10. The process of claim 8 wherein the sections are cooled to a temperature below about 10° C. before being dewatered. 
     
     
       11. The process of claim 10 wherein the curing is conducted at a temperature in the range of from about 100° C. to about 220° C. 
     
     
       12. The process of claim 11 wherein the sections of wood are of the same type, and have the same shape and size. 
     
     
       13. The process of claim 2 wherein the second temperature is in the range of from about 180° C. to about 200° C. 
     
     
       14. The process of claim 13 wherein the softening stage is conducted at a pressure which is higher than the equilibrium pressure at the operating temperature. 
     
     
       15. The process of claim 14 wherein there is substantially no temperature difference between the center and the outer parts of the sections. 
     
     
       16. The process of claim 15 wherein during the second part of the softening stage the temperature is maintained for a time in the range of from about 0.1 to about 0.75 hour. 
     
     
       17. The process of claim 16 wherein the curing is conducted at a temperature in the range of from about 140° C. to about 200° C. 
     
     
       18. The process of claim 17 wherein the sections to be treated have a moisture content in the range of from about 50% to about 60% by weight. 
     
     
       19. The process of claim 18 wherein the sections of wood are of the same type, and have the same shape and size.